versions – Optionally omit pieces of text

Stephan Bel­lan­toni’s ver­sion has
pro­vided pream­ble com­mands for se­lect­ing en­vi­ron­ments to be
in­cluded/ex­cluded. This pack­age does the same, but cor­rects,
im­proves, and ex­tends it in both im­ple­men­ta­tion and
func­tion.